The terracotta stakes are fitted with a wine bottle of full of water and stuck in the plant's soil. As the terracotta absorbs the water, it will slowly leak into the soil and keep the plant's roots moist.

A set of four is $20 and three sets of four are currently on sale for $40 from Napa Style. These also make a great, useful gift. Wrapped with a nice ribbon, a single Plant Nannie would be a great $5 gift. Via:notcot.org.